To improve aircraft performance, aircraft manufacturers are increasingly turning to composite materials (e.g., Kevlar, epoxy graphite, carbon laminate, carbon sandwich, fiberglass, etc.) rather than traditional aluminum materials for aircraft construction. For example, it has been common to employ an aluminum fuselage and wings in combination with composite materials used for control surfaces, engine nacelles, etc. However, newer aircraft are now being built with composite fuselage and wing materials. As an example, the Boeing 787 employs an all-composite fuselage, making it the first airliner in production to employ composite materials for fifty percent of its construction.
Aircraft, such as airliners, are often equipped with satellite communication (SATCOM) capabilities that require antenna devices to be mounted to an external surface of the aircraft. The UHF SATCOM frequency bands are defined as 244 to 270 MHz (10.2% bandwidth) downlink frequencies, and 292 to 317 MHz 8% bandwidth) uplink frequencies. Conventional ultra-high frequency (UHF) SATCOM antenna devices employ two antennas: a first antenna (e.g., quadrifilar helix or crossed dipole antenna) for high angle (overhead) UHF satellite communications, and a second monopole antenna for low angle (horizon) UHF satellite communications. Each one of these antenna devices tends to be bandwidth limited. The performance (i.e., VSWR, gain, etc.) of an antenna mounted on a composite surface is considerably different than the same antenna mounted on a metallic structure. Therefore, conventional aircraft communication antennas are mounted on metal aircraft surfaces (e.g., aluminum fuselage surfaces) rather than non-metallic composite surfaces of an aircraft that is of mixed metallic/composite material construction.
FIG. 1 illustrates one example of a planar UHF SATCOM antenna device 100 of the prior art that is coupled to a conductive metal surface 150 of an aircraft, and as may be contained within an aerodynamic enclosure such as a radome. As shown in FIG. 1, antenna device 100 includes a base plate 120 and a high angle UHF SATCOM dipole antenna structure that includes a first leg structure 102 and a second (floating) leg structure 104 that are coupled to a first UHF SATCOM feed 106 and a first UHF SATCOM ground 108. Conductive metal surface 150 of the aircraft acts as a ground plane for antenna device 100.
As shown in FIG. 1, a cylindrical feed member 117 (i.e., 0.141″ diameter coaxial cable having outer metallic shield 119 and inner center core 107 electrically coupled together with dielectric insulating material therebetween) is connected between first UHF SATCOM feed 106 and first leg 102 via conductor 109, and first UHF SATCOM ground 108 is directly connected to second antenna leg 104 through electrically conductive base plate 120. Each of first and second leg structures 102 and 104 are manufactured from a conductive outer skin of copper that surrounds a lightweight foam core. A capacitive director structure 116 is provided as shown and includes a conductive copper layer 114 that is separated from first and second leg structures 102 and 104 by a thin dielectric layer 112.
Still referring to FIG. 1, UHF SATCOM antenna device 100 also includes a low angle UHF SATCOM monopole antenna structure that includes a folded monopole antenna element 130 that is coupled to a second UHF SATCOM feed 136, with second UHF SATCOM ground 138 coupled to base plate 120 as shown. The terminal end of folded monopole antenna element 130 is spaced from base plate 120 by dielectric spacer 140 as shown. During operation, satellite communications are switched between high angle UHF SATCOM dipole antenna structure and low angle UHF SATCOM dipole antenna structure as needed based on satellite angle relative to the aircraft.